S8400/IA770 CM3.2 - Periodically, about 2-4 times a day, the alarm goes into a three tone alarm, lighting the alarm, calls waiting, and one other light. No errors or alarms coincide with this alarm, and console, ps, and port have been changed. The display is usually blank, but occassionally it will display an extension on the switch. The receptionist must hit "Cancel" to clear. Any ideas?